The goal of the research underway is to improve our understanding of the molecular genetics of hemophilia A. This is being accomplished using a radioimmunoassay to coagulant factor VIII (VIII:C) to search for molecular variants of the defective VIII:C molecule. This search will be conducted in affected, obligatory carriers and other members of hemophilia A kindred to determine if the molecular variant is inherited in a sex-linked Mendelian fashion within kindred. We will determine if molecular variants of VIII:C show qualitative antigenic differences as well as quantitative differences using a variety of alloantibodies to VIII:C. Finally, the usefulness of VIII:C antigen (VIII:CAg) determinations in carrier detection of hemophilia A will be determined.